Method and means for producing chromatographic capillary columns



March 8, 1966 HElNZ-HARDY NESS 3,233,759

METHOD AND MEANS FOR PRODUCING CHROMATOGRAPHIC CAPILLARY COLUMNS Filed Nov. 12, 1963 HEINZ-HARDY NES S INVENTOR.

United States Patent Office 3,238,759 Patented Mar. .8, 1966 8 Claims. (a. 72283) This invention relates to an improved method for producing capillary columns for gas chromatography. More specifically .the invention is an improved method of providing a granular solid substance as a layer embedded in the interior wall of a small diameter tube.

In United States patent application Serial No. 227,350, filed October 1, 1962, now Patent No. 3,182,394, a method for producing capillary columns for gas chromatography is disclosed and claimed. That application teaches a method of embedding granular solid material in the interior wall of a metallic capillary tube during the process in which the capillary is drawn from a larger diameter tubing. As taught therein, the solid material either may act as the separating substance (i.e., stationary phase) of a gas chromatographic column or may be coated with a liquid separating substance (i.e., the solid is merely a carrier substance).

The present invention relates to a particularly advantageous modification of this method. Specifically the present invention dilfers in that a plug, around which the tube is drawn through the drawing nozzle, is utilized; and the separating or carrier substance to be embedded is added to a lubricant which is introduced into the larger diameter tube behind the plug.

During the drawing process the lubricant and the separating or carrier substance is constantly and uniformly fed between the walls of the drawn tube and the plug, so as to be embedded in the walls of the tube as it is drawn through the drawing nozzle. By quantitatively regulating the concentration of the separating or carrier substance in the lubricant, the thickness of layer embedded on the tube walls may be varied. The lubricant may be removed by any convenient means (e.g., by solvent or heating) from the capillary tube after the drawing process has been completed.

To avoid excessive viscosity of the mixture, it is advantageous to use a lubricant of low (i.e., water-like) viscosity, since the viscosity of the mixture is increased by the added solid separating or carrier material. It is particularly expedient to use a drawing die with a conical bore narrowing in the direction of movement of the tube and a plug protruding into the bore. The plug preferably has a conical front portion, but the central cone angle of the plug is somewhat smaller than that of the conical bore so that a small, constantly narrowing annular channel is formed between the plug and the drawing nozzle of the die. Thus, a wedge effect is produced between the cone-shaped front portion of the plug and the interior wall of the tube (which is softened by the drawing process), and the granular solid material is therefore pressed into the plastic tube wall.

An object of the invention is to provide an improved method for producing a capillary tube with granular solid separating or carrier substance embedded in the interior wall of the tube, which tube is suitable for use as a gas chromatographic capillary column.

Another object of the invention is to provide an improved method of the type mentioned immediately above, which yields even and uniform thickness of the layer of embedded solid substance.

A further object of the invention is to provide an improved method of the type mentioned above, in which the thickness of the layer of embedded solid material may be readily varied (namely, by changing the proportionate amount of solid substance in the lubricant).

Other objects and advantages of the invention will become apparent to one skilled in the art upon reading this specification in conjunction with the accompanying drawing, in which the sole figure shows a single embodiment of how the inventive method may be performed.

In the drawing a die 10 forms a funnel-shaped drawing nozzle by being provided with a conical bore 11, which, in the forward direction (i.e., the direction of drawing of the tube), communicates with a cylindrical bore 12 corresponding to the desired outer diameter of the drawn tube. Tube 13 of relatively large diameter is sharpened at the end to bev drawn and insented through the drawing nozzle 11, 12, and a plug 14 is inserted in the tube 13. This plug consists of an approximately cylindrical body 15 with a spherical back end 16 and a conical front portion 17 terminating in a cylindrical pin 18. The diameter of body 15 is somewhat smaller than the internal diameter of tube 13' so that an annular channel 19 is formed between tube Walls and body 15. The central cone angle of the conical front pontion 17 is somewhat smaller than the cone angle of the bore 11 so that the annular channel 19 constantly narrows in the direction of drawing of the tube.

A lubricant 20 and the granular separating or carrier substance (which is to be embedded in the capillary tube wall) is introduced into the tube 13 behind plug 14. The tube 13 is then gripped with known mechanical means at the end protruding from the drawing nozzle and drawn through the drawing nozzle 11, 12. In so doing, lubricant (and the granular material) is constantly carried along from the walls of tube 13 into the annular chamber 19, since, as previously pointed out, its viscosity is low enough so that the mixture flows under these conditions. During the drawing process the granular separating or carrier substance is therefore gradually pressed into the tube walls which are in a softened or plastic condition during the drawing process. Tube 13 and material 20 tend to pull the plug 14 to the left in the drawing by friction; however, the plug 14 is, of course, unable to pass through the drawing nozzle 11, 12.

From the other side of drawing nozzle 11, 12 a tube 13' of smaller diameter is obtained in the inside walls of which the grains 21 of the separating or carrier material are embedded. Any undesirable lubricant remaining in tube 13' may be removed in any conventional manner, such as by evaporating it by heat or washing it out by means of any convenient (e.g., a relatively volatile) solvent.

Although a single embodiment of the invention has been illustrated and specifically described, certain changes will be obvious to one skilled in the art. For this reason, the invention is not limited to any of the exact details of the specific disclosed embodiment, but rather is defined solely by the scope of the appended claims.

I claim:

1. The improved method of producing capillary columns for use in gas chromatography of the type comprising a capillary tube having granular solid material embedded in the interior wall thereof, comprising:

forming a mixture of a lubricant and the granular solid material desired to be embedded in said capillary tube interior wall;

introducing said lubricant and granular solid material mixture into a larger diameter tubing;

drawing said larger diameter tubing to form a small diameter capillary tube under such conditions as to soften temporarily the interior wall of said capillary tube at the place of drawing;

and providing means inside said tubing adjacent said place of drawing to form an annular channel for guiding said mixture against said softened interior wall of said capillary tube;

whereby said mixture is caused to be in close contact with said softened interior wall so as to cause embedding of said granular solid material therein.

2. The improved method according to claim 1, in

which:

said lubricant has a low, water-like viscosity so that said mixture has a viscosity sufliciently low as to flow during the drawing process.

3. The improved method of claim 1, in which:

said introducing of said mixture is accompanied by a wedging action so as to press the granular solid material in intimate contact with said softened interior wall of said capillary tube.

4. The improved method according to claim 1, in

which:

said larger diameter tubing and therefore said drawn capillary tube is metallic.

5. The improved apparatus for producing capillary gas chromatographic columns of the type comprising a capillary tube having granular solid material embedded in theinterior wall thereof, comprising:

a die means having an opening which comprises a larger tapered part ending in a substantially cylindrical small diameter part, the larger end of the tapered part being adapted to receive a relatively large diameter tubing, and the smaller cylindrical part having a diameter equal to the outside diameter of the capillary tube desired to be produced;

a plug means, having a substantially cylindrical nose portion of outer diameter equal to the inner diameter of the capillary tube desired to be produced, said nose portion being adapted to be positioned in spaced relationship within said cylindrical part .of said opening in said die;

said plug means additionally comprising a tapered portion joining said nose portion with a substantially larger diameter body portion, said tapered portion having a taper generally similar to said tapered part of the opening in said die member and being adapted to be positioned in spaced relationship within said tapered part of said opening;

said plug means comprising a relatively large diameter body portion extending from the wider part of said tapered portion, said body portion having a diameter slightly less than the inside diameter of the relatively large tubing which is to be drawn down to form said capillary tube; the resulting space left between the outside of said body portion and the interior wall of said larger diameter tubing, and the space left between the outside of said tapered portion of said plug means and the wall forming the tapered part of said'opening in said die means each forming an annular channel for the introduction of a mixture comprising a lubricant and the solid granular material intended to be embedded in the interior wall of the capillary tube as it is formed; whereby the drawing through said die means causes the lubricant and solid granular material mixture to be:pulled 'by said tubing into the opening in said die member, and said tapered portion of said plug means causes the granular material to be guided to the interior wall of the capillary tube at that point in the die at which said interior wall is temporarily softened, so that said granular material is embedded in said capillary tube interior wall. 6. The improved apparatus according to claim 5, in which:

said generally similar shape of said tapered part of said die opening and of the tapered portion ofsaid plug means is conical. 7. The improved apparatus according to claim5, .in which:

said tapered'portion of said plug tapers at a somewhat lesser rate than the rate of taper of said .die opening tapered part, so that the annular channel formed between said plug and opening narrows in the direction of the drawing operation. 8. The improved apparatus according to claim 6, in which:

the central cone angle of said tapered plug portion is less than thecentral cone angle of said die opening tapered part, so that the'annular channel formed between said :plug and die opening, narrows in the direction of the drawingoperation.

References Cited by the Examiner UNITED STATES PATENTS 307,993 11/1884 Sharp 205-7 2,355,734 8/1944 Katz 2057 2,721,651 10/1955 Roth 205-- 7 0 CHARLES \V. LANHAM, Primary Examiner. 

1. THE IMPROVED METHOD OF PRODUCING CAPILLARY COLUMNS FOR USE IN GAS CHROMATOGRAPY OF THE TYPE COMPRISING A CAPILLARY TUBE HAVING GRANULAR SOLID MATERIAL EMBEDDED IN THE INTERIOR WALL THEREOF, COMPRISING: FORMING A MIXTURE OF A LUBRICANT AND THE GRANULAR SOLID MATERIAL DESIRED TO BE EMBEDDED IN SAID CAPILLARY TUBE INTERIOR WALL; INTRODUCING SAID LUBRICANT AND GRANULAR SOLID MATERIAL MIXTURE INTO A LARGER DIAMETER TUBING; DRAWING SAID LARGER DIAMETER TUBING TO FORM A SMALL DIAMETER CAPILLARY TUBE UNDER SUCH CONDITIONS AS TO SOFTEN TEMPORARILY THE INTERIOR WALL OF SAID CAPILLARY TUBE AT THE PLACE OF DRAWING; AND PROVIDING MEANS INSIDE SAID TUBING ADJACENT SAID PLACE OF DRAWING TO FORM AN ANNULAR CHANNEL FOR GUIDING SAID MIXTURE AGAINST SAID SOFTENED INTERIOR WALL OF SAID CAPILLARY TUBE; WHEREBY SAID MIXTURE IS CAUSED TO BE IN CLOSE CONTACT WITH SAID SOFTENED INTERIOR WALL SO AS TO CAUSE EMBEDDING OF SAID GRANULAR SOLID MATERIAL THEREIN. 